Method of producing polyoxytetramethylene glycol

ABSTRACT

In a process for the preparation of copolymers of tetrahydrofuran and but-2-yne-1,4-diol by catalytic polymerization of tetrahydrofuran, the polymerization is carried out over a heterogeneous acidic catalyst which has acid centers of acidity pK a  &lt;+2 in a concentration of at least 0.005 mmol/g of catalyst, in the presence of but-2-yne-1,4-diol. In particular, for the preparation of polyoxytetramethylene glycol, the copolymers are reacted in the presence of hydrogen over a hydrogenation catalyst.

The present invention relates to a process for the preparation ofcopolymers of tetrahydrofuran (THF) and but-2-yne-1,4-diol by catalyticpolymerization of THF. The present invention relates in particular to aprocess for the preparation of polyoxytetramethylene glycol.Polyoxytetramethylene glycol, also referred to as polytetrahydrofuran(PTHF), is produced worldwide and serves as an intermediate for thepreparation of polyurethane, polyester and polyamide elastomers, for thepreparation of which it is used as a diol component. The incorporationof PTHF into these polymers renders them soft and flexible, and PTHF istherefore also referred to as the soft segment component for thesepolymers.

The cationic polymerization of tetrahydrofuran (THF) with the aid ofcatalysts was described by Meerwein et al. (Angew. Chem. 72 (1960),927). Either premolded catalysts are used here as catalysts, or thecatalysts are produced in situ in the reaction mixture. This is done byproducing oxonium ions in the reaction medium with the aid of strongLewis acids, such as boron trifluoride, aluminum chloride, tintetrachloride, antimony pentachloride, iron(III) chloride or phosphoruspentafluoride, or by means of strong Bronsted acids, such as perchloricacid, tetrafluoroboric acid, fluorosulfonic acid, chlorosulfonic acid,hexachlorostannic(IV) acid, iodic acid, hexachloroantimonic(V) acid ortetrachloroferric(III) acid, and with the aid of reactive compoundsreferred to as promoters, such as alkylene oxides, eg. ethylene oxide,propylene oxide, epichlorohydrin, ortho-acid esters, acetals,α-haloethers, acetyl chloride, carboxylic anhydrides, thionyl chlorideor phosphoryl chloride, said oxonium ions initiating the polymerizationof the THF. From the large number of these catalyst systems, however,only a few have become industrially important, since some of them arehighly corrosive and/or lead to discolored PTHF products in thepreparation of PTHF, which only have limited use. Furthermore, many ofthese catalyst systems do not have the catalytic action in the truesense but have to be used in stoichiometric amounts, based on themacromolecule to be prepared, and are consumed during thepolymerization.

U.S. Pat. No. 3,358,042 describes the preparation of PTHF usingfluorosulfonic acid as the catalyst. A particular disadvantage of theuse of halogen-containing catalyst compounds is that they lead to theformation of halogenated byproducts during the PTHF preparation, whichbyproducts are very difficult to separate from the pure PTHF and have anadverse effect on its properties.

In the preparation of PTHF in the presence of the stated promoters,these promoters are incorporated into the PTHF molecule so that theprimary product of the THF polymerization is not PTHF but a PTHFderivative. For example, alkylene oxides are incorporated as comonomersinto the polymer, with the result that THF/alkylene oxide copolymershaving properties, in particular performance characteristics, whichdiffer from those of PTHF are formed.

The use of carboxylic anhydrides as promoters results primarily in theformation of PTHF diesters, from which PTHF must be liberated in afurther reaction, for example by hydrolysis or transesterification (cf.U.S. Pat. No. 2 499 725 and DE-A 27 60 272).

According to U.S. Pat. No. 5,149,862, sulfate-doped zirconium dioxide isused as an acidic heterogeneous polymerization catalyst which isinsoluble in the reaction medium. In order to accelerate thepolymerization, a mixture of acetic acid and acetic anhydride is addedto the reaction medium, since the polymerization takes place only veryslowly in the absence of these promoters and, for example, a conversionof only 6% is achieved during a period of 19 hours. This process resultsin the formation of PTHF diacetates, which then have to be convertedinto PTHF by hydrolysis or transesterification.

JP-A 83 028/1983 describes the polymerization of THF in the presence ofan acyl halide or carboxylic anhydride, a heteropolyacid being used asthe catalyst. PTHF diesters are likewise formed and have to behydrolyzed to PTHF.

PTHF diesters are also formed in the polymerization of chemicallypretreated THF with bleaching earth catalysts in the presence ofcarboxylic anhydrides, eg. acetic anhydride, according to EP-A-0 003112. A principle disadvantage of this THF polymerization process isassociated with the costs incurred for the use of acetic anhydride andits elimination from the PTHF derivative (methyl ester) formed as theprimary product.

If, on the other hand, the THF polymerization is carried out using wateras a telogen (chain-terminating substance), PTHF is formed directly.According to U.S. Pat. No. 4,120,903, PTHF can be prepared from THF andwater with the aid of superacidic Nafion® ion exchange resins. Thedisadvantage of this process is the high molecular weight of theresulting PTHF, which is about 10,000 Dalton. Such high molecular weightPTHF is to date of no industrial importance.

U.S. Pat. No. 4,568,775 and U.S. Pat. No. 4,658,065 describe,respectively, a process for the preparation of PTHF and thecopolymerization of THF with a polyol, heteropolyacids being used ascatalysts. The heteropolyacids are soluble to a certain degree in thepolymerization mixture and in the polymer and, since they causediscoloration of the PTHF product, must be removed therefrom byexpensive technical measures-addition of a hydrocarbon for precipitatingthe heteropolyacid, removal of the precipitated heteropolyacid andremoval of the added hydrocarbon.

In U.S. Pat. No. 4,303,782, zeolites are used for the preparation ofPTHF. However, the THF polymers obtainable by this process haveextremely high average molecular weights- M_(n) =250,000 to 500,000Dalton--and could not be used for the abovementioned intended uses.Accordingly, this process too is of no industrial importance. A furtherserious disadvantage is of this process is the low space-time yield (forexample 4% of PTHF in 24 hours), which is achieved with the zeolitesused therein.

All of the abovementioned processes for the direct preparation of PTHFhave, especially for PTHF in the molecular weight range of from 500 to3500 Dalton, which is of industrial interest, the disadvantage of lowspace-time yields in heterogeneous catalysis or the disadvantage ofexpensive removal of the catalyst in homogeneous catalysis.

It is an object of the present invention to provide a process whichmakes it possible to obtain PTHF in high space-time yields, ie. withhigh selectivity in conjunction with high THF conversion, and withsimple removal of the catalyst.

We have found that this object is achieved, surprisingly, bypolymerizing tetrahydrofuran over a strongly acidic heterogeneouscatalyst in the presence of but-2-yne-1,4-diol and then catalyticallyhydrogenating the polyoxytetramethylene glycols containing C--C triplebonds to give polyoxytetramethylene glycol. The course of the reactioncan be described by the following equation, only one of the possiblecopolymers being indicated as a reaction product of the reaction of THFwith but-2-yne-1,4-diol. ##STR1## The present invention thereforerelates to a process for the preparation of polyoxytetramethyleneglycols or copolymers of THF and but-2-yne-1,4-diol by catalyticpolymerization of THF, the polymerization being carried out over aheterogeneous acidic catalyst which has acid centers of acidity pK_(a)<+2 in a concentration of at least 0.005 mmol/g of catalyst, in thepresence of but-2-yne-1,4-diol. The present invention relates inparticular to a process for the preparation of polyoxy-tetramethyleneglycol, the copolymers of THF and but-2-yne-1,4-diol orpolyoxytetramethylene glycols, prepared according to the invention andcontaining triple bonds, being converted over a hydrogenation catalystin the presence of hydrogen at from 20 to 300° C. and from 1 to 300 bar.Preferred embodiments of the invention are defined in the subclaims.

According to the invention, supported catalysts which comprise an oxidecarrier, contain oxygen-containing molybdenum or tungsten compounds ormixtures of such compounds as catalytically active compounds andfurthermore, if desired, may additionally be doped with sulfate orphosphate groups are preferably used as polymerization catalysts. Forconversion into their catalytically active form, the supported catalystsare subjected to calcination at from 500 to 1000° C. after the precursorcompounds of the catalytically active, oxygen-containing molybdenumand/or tungsten compounds have been applied to the carrier, the carrierand the precursor compound being converted into the catalysts which canbe used according to the invention.

Suitable oxide carriers are, for example, zirconium dioxide, titaniumdioxide, hafnium oxide, yttrium oxide, iron(III) oxide, alumina, tin(IV)oxide, silica, zinc oxide and mixtures of these oxides. Zirconiumdioxide and/or titanium dioxide are particularly preferred.

The catalysts which may be used according to the invention contain ingeneral from 0.1 to 50, preferably from 1 to 30, particularly preferablyfrom 5 to 20, % by weight of the catalytically active, oxygen-containingcompounds of molybdenum or of tungsten or of the mixtures of thecatalytically active, oxygen-containing compounds of these metals, basedin each case on the total weight of the catalyst, and, since thechemical structure of the catalytically active, oxygen-containingcompounds of molybdenum and/or of tungsten is not known exactly to datebut can only be postulated, for example from the data of the IR spectraof the catalysts which can be used according to the invention, it iscalculated in each case as MoO₃ or WO₃.

In principle, in addition to containing the catalytically active,oxygen-containing molybdenum and/or tungsten compounds, the novelcatalysts may also be doped with from 0.05 to 10, preferably from 0.1 to5, in particular from 0.25 to 3, % by weight, based in each case on thetotal weight of the catalyst, of oxygen-containing sulfur- and/orphosphorus-containing compounds. Since the chemical form in which thesesulfur- or phosphorus-containing compounds are present in the preparedcatalyst is likewise unknown, the contents of these groups in thecatalyst are calculated together as SO₄ or PO₄.

For the preparation of the novel catalysts, hydroxides of the relevantcarrier components are as a rule used as starting materials. Where thesehydroxides are commercially available, hydroxides obtainable on themarket may be used as starting materials for the preparation of theoxide carriers, but preferably the oxide carriers are prepared usingfreshly precipitated hydroxides, which, after their precipitation, aregenerally dried at from 20 to 350° C., preferably from 50 to 150° C., inparticular from 100 to 120° C., at atmospheric or reduced pressure.

In general, the water-soluble or hydrolyzable salts of the elementsconstituting the carrier, for example their halides, preferably theirnitrates or carboxylates, in particular their acetates, are used asstarting compounds for the preparation of these hydroxides. Suitablestarting compounds for the pre-cipitation of these hydroxides are, forexample, zirconyl chloride, zirconyl nitrate, titanyl chloride, titanylnitrate, yttrium nitrate, yttrium acetate, aluminum nitrate, aluminumacetate, iron(III) nitrate, tin(IV) halides, in particular tin(IV)chloride, zinc nitrate or zinc acetate. The corresponding hydroxides arepre-cipitated from the solutions of these salts preferably by means ofaqueous ammonia solution. Alternatively, the hydroxides can be obtainedby adding dilute or weak acids, such as acetic acid, to water-solublehydroxo complexes of the relevant metals until the relevant hydroxide isprecipitated. It is also possible to obtain the hydroxides by hydrolysisof organometallic compounds, for example the alcoholates of the relevantmetals, such as zirconium tetraethylate, zirconium tetraisopropylate,titanium tetramethylate, titanium tetraisopropylate, etc.

In general, a gelatinous precipitate is formed during the precipitationof these hydroxides, which precipitate gives an X-ray amorphous powderafter drying. It is possible that these X-ray amorphous precipitates arecomposed not only of the hydroxides of the relevant metals butadditionally of a large number of other hydroxyl-containing compounds,for example hydrated oxides, polymeric, water-insoluble hydroxocomplexes, etc. However, since the exact chemical composition of theseprecipitates cannot be determined, for the purposes of this applicationit will be assumed for the sake of simplicity that they are thehydroxides of the stated metals. For the purposes of this application,the term hydroxides is thus an overall designation for thehydroxylcontaining precipitates obtained in the abovementionedprecipitation methods.

When silica is used as the oxide carrier, the starting material used forthe preparation of the catalysts which can be used according to theinvention is preferably freshly precipitated silica, which can beobtained, for example, by acidifying a waterglass solution, and which isadvantageously dried before further processing, as described above forthe hydroxide precipitates.

The precursor compounds of the catalytically active, oxygen-containingmolybdenum and/or tungsten compounds are applied to the hydroxides ofthe carrier components or the silica, which are prepared in this mannerand are also referred to as carrier precursors in this application, theapplication preferably being effected by impregnation with an aqueoussolution of these pre-cursor compounds. For example, the water-solublesalts of tungstic acid (H₂ WO4), as formed, for example, on dis-solutionof tungsten trioxide in aqueous ammonia, ie. the monotungstates, and theisopolytungstates formed therefrom on acidification, for example theparatungstates or metatungstates, and the water-soluble salts ofmolybdic acid (H₂ MoO₄), as formed, for example, on dissolution ofmolybdenum trioxide in aqueous ammonia, and the isopolymolybdates formedtherefrom on acidification, in particular the metamolybdates andparamolybdates, can be used as water-soluble precursor compounds of thecatalytically active, oxygen-containing tungsten or molybdenumcompounds. Preferably, the ammonium salts of these tungstic and molybdicacids are applied as pre-cursor compounds to the hydroxides of thecarrier components or to the silica by impregnation. Regardingnomenclature, composition and preparation of the molybdates,isopolymolybdates, tungstates and isopolytungstates, reference may bemade to Rompps Chemie-Lexikon, 8th edition, Volume 4, pages 2659-2660,Francksche Verlagsbuchhandlung, Stuttgart, 1985; Rompps Chemie-Lexikon,8th edition, Volume 6, pages 4641-4644, Stuttgart 1988, andComprehensive Inorganic Chemistry, 1st edition, Vol. 3, pages 738-741and 766-768, Perganon Press, New York, 1973. Instead of theabovementioned molybdenum and tungsten precursor compounds of thecatalytically active molybdenum and tungsten compounds, respectively, itis also possible to use heteropolyacids of molybdenum and of tungsten,such as 12-tungstatosilicic acid (H₄ [Si{W₁₂ O₄₀ }]26H₂ O) or12-molybdatosilicic acid, or their water-soluble salts, preferably theirammonium salts, for applying the molybdenum or tungsten to thehydroxide, ie. hydroxyl-containing, carrier precursor. The hydroxides ofthe particular carrier components used, which hydroxides have beenimpregnated in this manner, and the impregnated silica are generallydried at from 80 to 350° C., preferably from 90 to 150° C., atatmospheric or reduced pressure.

It is also possible to introduce the stated precursor compounds of thecatalytically active, oxygen-containing molybdenum or tungsten compoundsinto the subsequently obtained catalyst by thorough mixing with one ormore of the stated hydroxides. The calcination of the carrierprecursors, which have been treated in this manner, to give thecatalysts which can be used according to the invention is carried out inthe same manner as for the carrier precursors impregnated with theseprecursor compounds. However, the impregnation method is preferably usedfor the preparation of the catalysts which can be used according to theinvention.

The catalyst precursors impregnated and dried in this manner areconverted into the finished catalysts by calcination in the air at from500 to 1000° C., preferably from 550 to 900° C., particularly preferablyfrom 600 to 800° C. In the course of the calcination, the hydroxides ofthe carrier components and the silica are converted into the oxidecarrier, and the precursor compounds of the catalytically active,oxygen-containing molybdenum or tungsten compounds, which have beenapplied to said carrier by impregnation, are converted into thecatalytically active components. Calcination at these high temperaturesis critical for achieving a high conversion and hence a high space-timeyield in the THF polymerization. At lower calcination temperatures, thecatalysts also produce THF polymerization, but only with uneconomicallylow conversions. On the basis of IR investigations of catalysts preparedin this manner, Yinyan et al., Rare Metals 11 (1992), 185, presume that,in the case of tungsten-doped zirconium oxide supported catalysts, theprecursor compound of the catalytically active, oxygen-containingtungsten compound, which precursor compound has been applied to thezirconium hydroxide by impregnation, forms a chemical bond with thehydroxyl groups of the carrier precursor at the high calcinationtemperatures used, resulting in the formation of the catalyticallyactive, oxygen-containing tungsten compound, which differs substantiallywith regard to its chemical structure and chemical activity, inparticular its catalytic properties, from oxygen-containing tungstencompounds merely adsorbed onto the zirconium dioxide carrier. Thissituation is also assumed for the molybdenum-containing supportedcatalysts which can be used according to the invention.

As stated above, supported catalysts which, apart from molybdenum and/ortungsten, are additionally doped with sulfur- and/orphosphorus-containing compounds may also advantageously be used in thenovel process. These catalysts are prepared in a manner similar to thatdescribed above for the catalysts containing only molybdenum and/ortungsten compounds, sulfur- and/or phosphorus-containing compoundsadditionally being applied by impregnation to the hydroxides of thecarrier components, prepared in a similar manner, or to the silica. Thesulfur- and/or phosphorus compounds can be applied to the carriersimultaneously with the application of the molybdenum and/or tungstencomponent, or thereafter. The sulfur and/or phosphorus components areadvantageously prepared by impregnating the hydroxides of the carriercomponents or the silica with an aqueous solution of a compoundcontaining sulfate or phosphate groups, for example sulfuric acid orphosphoric acid. Solutions of water-soluble sulfates or phosphates mayalso advantageously be used for the impregnation, ammonium sulfates orammonium phosphates being particularly preferred. A further method forapplying the phosphorus-containing precursor compounds together with themolybdenum- or tungsten-containing precursor compounds to the hydroxidecarrier precursor is to treat the hydroxide carrier precursors withphosphorus-containing heteropolyacids by the methods described above.Examples of such heteropolyacids are 12-tungstatophosphoric acid (H₃PW₁₂ O₄₀ ·xH₂ O) and 12-molybdatophosphoric acid (H₃ PMo₁₂ O₄₀ ·xH₂ O).Heteropolyacids of molybdenum or of tungsten with organic acids ofphosphorus, for example phosphonic acids, may also be used for thispurpose. The stated heteropolyacids may also be used for this purpose inthe form of their salts, preferably as ammonium salts.

During the calcination under the abovementioned conditions, theheteropolyacids are decomposed into the catalytically active,oxygen-containing molybdenum or tungsten compounds.

Some of the catalysts which can be used according to the invention areknown, and their preparation is described, for example, in JP-A 288339/1989, JP-A 293 375/1993, J. Chem. Soc., Chem. Commun. (1987), 1259,and Rare Metals 11 (1992), 185. The catalysts have been used to datepredominantly only in petrochemical processes, for example as catalystsfor alkylations, isomerizations and the cracking of hydrocarbons, ie.processes which are not related to the novel process.

In addition to the abovementioned tungsten- and molybdenum-containingzirconium dioxides, sulfate-doped zirconium dioxides may also be used aspolymerization catalysts. The properties and the preparation ofsulfate-doped zirconium dioxides are described, for example, in M. Hinoand K. Arata, J. Chem. Soc., Chem. Comm. (1980), 851.

Bleaching earths, too, may be used as polymerization catalysts in thenovel process. In mineralogical terms, bleaching earths or Fuller'searths belong to the montmorillonite class. These are hydrated aluminumhydrosilicates which occur naturally and in which some of the aluminumions may have been replaced by iron, magnesium or other alkali metals oralkaline earth metals. The ratio of silica to oxides of divalent ortrivalent metals in these minerals is in general 4:1. The commercialproducts, which are generally activated by acid treatment and have awater content of from 4 to 8% by weight, based on the total weight, areused in large amounts for refining edible oils, fats and mineral oilsand as adsorbents and fillers.

Bleaching earths as obtainable under the name Tonsil® of the types K 10,KSF-O, KO and KS from Sud-Chemie AG, Munich, are particularly preferablyused in the novel process.

Zeolites, too, may be used as polymerization catalysts in the novelprocess. Zeolites are defined as a class of aluminum silicates which,owing to their particular chemical structure, form three-dimensionalnetworks having defined pores and channels in the crystal. Depending ontheir composition, in particular the SiO₂ -Al₂ O₃ molar ratio, and theircrystal structure, which is determined not only by the stated atomicratio but also by the method of preparation of the zeolites, adistinction is made between various zeolite types, some of whose namesare attributable to naturally occurring zeolite minerals of similarcomposition and structure, for example the faujasites, mordenites orclinoptilolites, or which are assigned acronyms where there are nospecific analogs in nature for the synthesized zeolites or where thesezeolites form a structural subclass of the naturally occurring zeolites,for example the Y and X zeolites belonging to the faujasite type or thezeolites having a pentasil structure, such as ZSM-5, ZSM-11 or ZBM-10.Summaries of the chemical composition of the zeolites, theirthree-dimensional and chemical structure and their method of preparationappear in, for example, D. W. Breck, Zeolite Molecular Sieves, Wiley,New York, 1974.

The zeolites which are suitable for the novel process have an SiO₂ /Al₂0₃ molar ratio of from 4:1 to 100:1, preferably from 6:1 to 90:1,particularly pre-ferably from 10:1 to 80:1. The primary crystallites ofthese zeolites have a particle size of up to 0.5 μm, preferably up to0.1 μm, particularly preferably up to 0.05 μm.

The zeolites which may be used as polymerization catalysts in the novelprocess are employed in the H form. In this form, acidic OH groups arepresent in the zeolite. If the zeolites are not obtained in the H formin their preparation, they can be readily converted into thecatalytically active H form, for example by treatment with, for example,mineral acids, such as hydrochloric acid, sulfuric acid or phosphoricacid, or by thermal treatment of suitable precursor zeolites whichcontain, for example, ammonium ions, for example by heating to 450-600°C., preferably 500-550° C.

All zeolites which meet the abovementioned requirements may be used aspolymerization catalysts in the novel process. Examples of these are thezeolites of the mordenite group and those of the faujasite group, inparticular the synthesized X and Y zeolites. Aluminophosphates orsilicoaluminophosphates having a zeolite structure may also be used.

Zeolites having pentasil structure, for example ZSM-5, ZSM-11 and ZBM-10zeolites, are particularly preferably used. Among these zeolites of thepentasil group, those which in turn have particularly advantageousproperties are the zeolites which were prepared in such a way that theyare substantially free of alkali metal compounds, ie. their alkali metalcontent is in general less than 50 ppm by weight. The preparation ofalkali-free ZBM-10 zeolites is described in EP-A-0 007 081, and a methodfor the preparation of substantially alkali-free ZSM-5 zeolites isdescribed by Muller et al. in Occelli, Robson (Eds.), Zeolite Synthesis,A. C. S. Symp. Series 398 (1989), 346. The zeolites prepared by thesemethods are present in the H form after a heat treatment at, forexample, from 500 to 600° C.

In addition to zeolites, polymers containing α-fluorosulfonic acidgroups may also be used as polymerization catalysts. Perfluorinatedpolymers which contain α-fluorosulfonic acid groups and are available,for example, under the name Nafion® from E.I. du Pont de Nemours andCompany are preferred.

The catalysts which can be used according to the invention may beemployed in the novel process in the form of powder, for example whenthe process is carried out by the suspension procedure, oradvantageously as moldings, for example in the form of cylinders,spheres, rings, spirals or chips, particularly in a fixed-bedarrangement of the catalyst, which arrangement is preferred when, forexample, loop reactors are used or the process is carried out bycontinuous methods.

In principle, any desired THF may be used as a monomer. Commercial THFor THF prepurified by acid treatment (cf. EP-A-0 003 112) or bydistillation is preferably used.

According to the invention, but-2-yne-1,4diol is used as a telogen, ie.as a substance which effects chain termination in the polymerizationreaction.

The telogen is fed to the polymerization advantageously as a solution inTHF. Since the telogen stops the polymerization, the average molecularweight of the unsaturated PTHF copolymer can be controlled by means ofthe amount of telogen used. The larger the amount of telogen containedin the reaction mixture, the lower is the average molecular weight ofthe unsaturated PTHF copolymer. Depending on the telogen content of thepolymerization mixture, the relevant PTHF copolymers having averagemolecular weights of from 250 to 10,000 can be prepared in a controlledmanner. The novel process is preferably used for preparing the relevantPTHF copolymers having average molecular weights of from 500 to 5000,particularly preferably from 650 to 3500, Dalton. For this purpose, thetelogen is added in amounts of from 0.04 to 17, preferably from 0.2 to8, particularly preferably from 0.4 to 4, mol %, based on the amount ofTHF used.

The polymerization is carried out in general at from 0 to 100° C.,preferably from 25° C. to the boiling point of the THF. The pressureused is as a rule not critical for the result of the polymerization, andthe procedure is therefore generally carried out at atmospheric pressureor under the autogenous pressure of the polymerization system.

In order to avoid the formation of ether per-oxides, the polymerizationis advantageously carried out under an inert gas atmosphere. The inertgases used may be, for example, nitrogen, hydrogen, carbon dioxide orthe noble gases, nitrogen being preferably employed.

The polymerization stage of the novel process can be carried outbatchwise or continuously, the continuous procedure generally beingpreferred for economic reasons.

In the batchwise procedure, the reactants THF and but-2-yne-1,4-diol andthe catalyst are generally reacted in a stirred kettle or loop reactorat the stated temperatures until the desired conversion of the THF isreached. The reaction time may be from 0.5 to 40, preferably from 1 to30, hours, depending on the amount of catalyst added. For thepolymerization, the catalysts are added in general in an amount of from1 to 90, preferably from 4 to 70, particularly preferably from 8 to 60,% by weight, based on the weight of the THF used.

For working up in the case of the batchwise procedure, the dischargedreaction mixture is separated from the catalyst suspended therein,advantageously by filtration, decanting or centrifuging.

The discharged polymerization mixture freed from the catalyst isgenerally worked up by distillation, unconverted THF advantageouslybeing distilled off in a first stage. In a second purification stage,low molecular weight PTHF can, if desired, then be separated from thepolymer by distillation at reduced pressure and can be recycled to thereaction. Alternatively, volatile THF oligomers can be depolymerized,for example by the process of DE-A 30 42 960, and recycled to thereaction in this manner.

In a preferred embodiment of the invention, the conversion of thecopolymers containing C--C triple bonds and comprising THF andbut-2-yne-1,4-diol into PTHF is carried out by catalytic hydrogenation.

When carrying out the hydrogenation, the copolymers, containing C--Ctriple bonds, and hydrogen are reacted over a hydrogenation catalyst atin general from 1 to 300, preferably from 20 to 250, in particular from40 to 200, bar and at from 20 to 300° C., preferably from 60 to 200° C.,particularly preferably from 100 to 160° C., to givepolyoxytetramethylene glycol.

The hydrogenation can be carried out without a solvent or,advantageously, in the presence of a solvent which is inert under thereaction conditions. Such solvents may be, for example, ethers, such astetrahydrofuran, methyl tert-butyl ether or di-n-butyl ether, alcohols,such as methanol, ethanol, propanol, isopropanol, butanol, isobutanol ortert-butanol, hydrocarbons, such as n-hexane, n-heptane or n-octane, andN-alkyllactams, such as N-methylpyrrolidone or N-octylpyrrolidone. Apreferred solvent is tetrahydrofuran. The reacted polymerizationmixtures obtained after the polymerization catalyst has been separatedoff are particularly preferably hydrogenated.

In general, all catalysts which are suitable for hydrogenating C--Ctriple bonds may be used as hydrogenation catalysts in the novelprocess. Hydrogenation catalysts which dissolve in the reaction mediumto give a homogeneous solution, as described, for example, inHouben-Weyl, Methoden der Organischen Chemie, Volume IV/lc, pages 16 to26, may be used.

However, heterogeneous hydrogenation catalysts, ie. those hydrogenationcatalysts which are essentially insoluble in the reaction medium, arepreferably used in the novel process. In principle, virtually allhetero-geneous hydrogenation catalysts may be used for hydro-genatingthe C--C triple bonds of the copolymers to C--C single bonds. Amongthese hydrogenation catalysts, those which contain one or more elementsof group Ib, VIIb and VIIb of the Periodic Table of Elements, inparticular nickel, copper and/or palladium, are preferred.

In addition to these components and, if required, a carrier, thesecatalysts may contain one or more other elements, such as chromium,tungsten, molybdenum, manganese and/or rhenium. Depending on thepreparation, oxidized phosphorus compounds, for example phosphates, mayalso be contained in the catalysts.

Heterogeneous hydrogenation catalysts which consist of metals inactivated, finely divided form having a large surface area, for exampleRaney nickel, Raney copper or palladium sponge, may be used in the novelprocess.

For example, precipitated catalysts may also be used in the novelprocess. Such catalysts can be prepared by precipitating theircatalytically active components from their salt solutions, in particularfrom the solutions of their nitrates and/or acetates, for example byadding alkali metal and/or alkaline earth metal hydroxide and/orcarbonate solutions, as, for example, sparingly soluble hydroxides,hydrated oxides, basic salts or carbonates, then drying the precipitatesobtained and thereafter converting them by calcination at in generalfrom 300 to 700° C., in particular from 400 to 600° C., into therelevant oxides, mixed oxides and/or mixed-valency oxides, which arereduced by treatment with hydrogen or with a hydrogen-containing gas at,as a rule, from 100 to 700° C., in particular from 150 to 400° C., tothe relevant metals and/or oxide compounds of lower oxidation state andare converted into the actual, catalytically active form. As a rule,reduction is continued until no more water is formed.

In the preparation of precipitated catalysts which contain a carrier,the precipitation of the catalytically active components may be effectedin the presence of the relevant carrier. However, the catalyticallyactive components can advantageously also be precipitated simultaneouslywith the carrier from the relevant salt solutions.

Furthermore, supported catalysts prepared in a conventional manner andcontaining one or more of the abovementioned catalytically activeelements may also be used as heterogeneous hydrogenation catalysts inthe novel process. Such supported catalysts are advantageously preparedby impregnating the carrier with a metal salt solution of the relevantelements, followed by drying and calcination at in general from 300 to700° C., preferably from 400 to 600° C., and reduction in ahydrogen-containing gas stream. The impregnated carrier is generallydried at from 20 to 200° C., preferably from 50 to 150° C., atatmospheric or reduced pressure. Higher drying temperatures are alsopossible. The reduction of the catalytically active catalyst componentsis carried out in general under the conditions stated above for theprecipitated catalysts.

In general, the oxides of the alkaline earth metals, of aluminum and oftitanium, zirconium dioxide, silica, kieselguhr, silica gel, aluminas,silicates, such as magnesium or aluminum silicates, barium sulfate oractive carbon may be used as carriers. Preferred carriers are zirconiumdioxide, aluminas, silica and active carbon. It is of course alsopossible to use mixtures of different carriers as the carrier forcatalysts which can be used in the novel process.

Hydrogenation catalysts which are preferably used in the novel processare Raney nickel, Raney copper, palladium sponge, impregnated supportedcatalysts, such as palladium on active carbon, palladium on alumina,palladium on silica, palladium on calcium oxide, palladium on bariumsulfate, nickel on alumina, nickel on silica, nickel on zirconiumdioxide, nickel on titanium dioxide, nickel on active carbon, copper onalumina, copper on silica, copper on zirconium dioxide, copper ontitanium dioxide, copper on active carbon or nickel and copper onsilica, and carrier-containing precipitated catalysts, such as Ni/Cu onzirconium dioxide, Ni/Cu on alumina or Ni/Cu on titanium dioxide.

Raney nickel, the abovementioned palladium supported catalysts, inparticular palladium on alumina or palladium on a carrier comprisingalumina and calcium oxide, and nickel and copper on precipitatedcatalysts containing a carrier, in particular nickel and copper onzirconium dioxide catalysts, are particularly preferably used in thenovel hydrogenation process for the preparation of polytetrahydrofuran.

The palladium supported catalysts contain in general from 0.2 to 10,preferably from 0.5 to 5, % by weight, calculated as Pd and base d onthe total weight of the catalyst, of palladium. The alumina/calciumoxide carrier for the palladium supported catalysts may contain ingeneral up to 50, preferably up to 30, % by weight, based on the weightof the carrier, of calcium oxide.

Further preferred supported catalysts are nickel and copper on silicacatalysts having a nickel content of in general from 5 to 40, preferablyfrom 10 to 30, % by weight, calculated as NiO, a copper content of ingeneral from 1 to 15, preferably from 5 to 10, % by weight, calculatedas CuO, and an SiO2 content of in general from 10 to 90, preferably from30 to 80, % by weight, based in each case on the total weight of theunreduced oxide catalyst. These catalysts may additionally contain from0.1 to 5% by weight, calculated as Mn₃ O₄, of manganese and from 0.1 to5% by weight, calculated as H₃ PO₄, of phosphorus, based in each case onthe total weight of the unreduced oxide catalyst. Of course, theabovementioned contents of catalyst components sum to a total content of100% by weight of these components in the catalyst. These catalysts areadvantageously prepared by impregnating silica moldings with saltsolutions of the catalytically active components, for example withsolutions of their nitrates, acetates or sulfates, then drying theimpregnated carriers at from 20 to 200° C., preferably from 100 to 150°C., under atmospheric or reduced pressure, calcining at from 400 to 600°C., preferably from 500 to 600° C., and reducing withhydrogen-containing gases. Such catalysts are disclosed, for example, inEP-A-295 435.

The precipitated catalysts comprising nickel and copper on zirconiumdioxide may contain in general from 20 to 70, preferably from 40 to 60,% by weight, calculated as NiO, of nickel, in general from 5 to 40,preferably from 10 to 35, % by weight, calculated as CuO, of copper andin general from 25 to 45% by weight of zirconium dioxide, based in eachcase on the total weight of the unreduced oxide catalyst. In addition,these catalysts may contain from 0.1 to 5% by weight, calcula-ted asMoO₃ and based on the total weight of the unreduced oxide catalyst, ofmolybdenum. Such catalysts and their preparation are disclosed in U.S.Pat. No. 5,037,793, which is hereby incorporated by reference.

The precipitated catalysts as well as the supported catalysts can alsobe activated in situ in the reaction mixture by the hydrogen presentthere. In a preferred embodiment of the invention, however, thecatalysts are reduced with hydrogen at from 20 to 300° C., preferablyfrom 80 to 250° C., before being used.

The hydrogenation stage of the novel process may be carried out eithercontinuously or batchwise. In the continuous procedure, it is possibleto use, for example, tube reactors in which the catalyst isadvantageously arranged in the form of a fixed bed over which thereaction mixture can be passed by the liquid phase or trickle-bedmethod. In the batchwise procedure, either simple stirred reactors or,advantageously, loop reactors may be used. When loop reactors are used,the catalyst is advantageously arranged in the form of a fixed bed. Thehydrogenation in the novel process is preferably carried out in theliquid phase.

The hydrogenation product polytetrahydrofuran (PTHF) is generallyisolated from the discharged hydrogenation mixture in a conventionalmanner, for example by distilling off the solvent contained in saidhydrogenation mixture and any other low molecular weight compoundspresent.

The novel process gives polytetrahydrofuran having a very low colornumber in high space-time yields and with simple removal of thecatalyst. At the same time, the polytetrahydrofuran prepared accordingto the invention has a molecular weight of from 500 to 3500, a rangewhich is of industrial interest.

In a further embodiment of the invention, the C--C triple bonds of thecopolymers of THF and but-2-yne-1,4-diol are converted into C--C doublebonds by partial hydrogenation, resulting in a polymer which correspondsto a THF/but-2-yne-1,4-diol copolymer in its chemical structure. SuchTHF/but-2-yne-1,4-diol copolymers are used, for example, as diolcomponents for the preparation of radiation-curable polyurethane andpolyester finishes.

The catalysts stated above for the hydrogenation of the C--C triplebonds to C--C single bonds may be used for hydrogenating the C--C triplebonds to C--C double bonds, but in general it should be ensured that theamount of hydrogen used for the partial hydrogenation does not exceedthe stoichiometric amount of hydrogen required for the partialhydrogenation of the C--C triple bonds to C--C double bonds.

The partial hydrogenation of the C--C triple bonds to C--C double bondsis preferably carried out using partially poisoned hydrogenationcatalysts, for example Lindlar palladium, which can be prepared byimpregnation of a carrier, eg. calcium carbonate, with a water-solublepalladium compound, eg. Pd(NO₃)₂, reduction of the applied palladiumcompound with, for example, hydrogen to give palladium metal andsubsequent partial poisoning of the resulting palladium supportedcatalyst with a lead compound, eg. lead(II) acetate. Such Lindlarcatalysts are commercially available.

Other preferred, partially poisoned palladium catalysts are thecatalysts which are described in German Patent Application No. P 43 33293.5 and which can be prepared by successive gas-phase deposition offirst palladium and then lead and/or cadmium onto a woven metal wirefabric or a metal foil.

The partial hydrogenation of the C--C triple bonds of thetetrahydrofuran/but-2-yne-1,4-diol copolymers to C--C double bonds iscarried out in general at from 0 to 100° C., preferably from 0 to 50°C., particularly preferably from 10 to 30° C., and at from I to 50,preferably from 1 to 5, in particular from 2 to 3, bar. The hydrogen ispreferably used in the stoichiometric amount required for the partialhydrogenation of the C--C triple bonds. If it is not intended tohydrogenate all C--C triple bonds to double bonds, the hydrogen may alsobe introduced in an amount which is smaller than the stoichiometricamount. The hydrogenation can be carried out either batchwise, forexample in stirred kettles using suspension catalysts, or continuously,for example in tube reactors with a fixed-bed catalyst.

The examples which follow illustrate the invention and constitutepreferred embodiments of the invention.

Preparation of the catalysts

Catalyst A

Pulverulent bleaching earth K 10 (acid-treated montnorillonite fromSud-Chemie) which was additionally calcined for 2 hours at 350° C. wasused as catalyst A.

Catalyst B

Bleaching earth K10 in powder form from Sud-Chemie was likewise used asstarting material for catalyst B and was molded to give 2.5 mmextrudates and then calcined at 350° C.

Catalyst C

Catalyst C was prepared by adding 2600 g of zirconium hydroxide to 2260g of a 26.5% strength by weight MoO₃ solution in 12% strength ammonia.This mixture was kneaded for 30 minutes and then dried for 16 hours at120° C. The dried material was kneaded with 40 g of 75% strengthphosphoric acid and 1.4 l of water for 30 minutes. Thereafter, dryingwas carried out for 2 hours at 120° C. The powder formed after sievingwas pelletized and the resulting pellets were then calcined at 600° C.for 2 hours. The catalyst had a molybdenum content of 20% by weight,calculated as molybdenum trioxide, and a phos-phorus content of 1% byweight, calculated as PO₄, based on the total weight of the catalyst.

Catalyst D

Catalyst D was prepared by adding 2600 g of zirconium hydroxide to asolution of 640 g of tungstic acid (H₂ WO₄) in 3470 g of 25% strengthammonia solution. This mixture was kneaded for 30 minutes and then driedfor 2 hours at 120° C. The powder formed after sieving was pelletizedand the resulting pellets (3×3 mm) were then calcined at 625° C. Thecatalyst had a tungsten content of 20% by weight, calculated as tungstentrioxide and based on the total weight of the catalyst.

Catalyst E

Catalyst E was prepared by adding 1600 g of zirconium hydroxide to asolution of 425 g of tungstic acid and 200 g of ammonium sulfate in 3470g of 25% strength ammonia solution. This mixture was kneaded for 30minutes and then dried for 2 hours at 120° C. The powder formed aftersieving was pelletized and the resulting pellets were then calcined at850° C. for 2 hours. The catalyst had a tungsten content of 18% byweight, calculated as tungsten trioxide, and a sulfur content of 7% byweight, calculated as SO₄, based on the total weight of the catalyst.

Catalyst F

Catalyst F was prepared by a preparation method due to M. Hino and K.Arata, J. Chem. Soc., Chem. Comm. (1980), 851, zirconium hydroxide beingprecipitated from an aqueous zirconyl nitrate solution by addingammonia. The precipitated zirconium hydroxide was dried at 100° C.,kneaded with 1N sulfluric acid and then molded to give 3×3 mm pellets.The pellets were dried at 100° C. and calcined at 550° C. for 2 hours.The catalyst had a sulfur content of 6% by weight, calculated as SO₄ andbased on the total weight of the catalyst.

Determination of the acidity of the catalysts

The acidity of the catalysts A to F was determined as described by K.Tanabe in Catalysis: Science and Technology (eds. J. R. Anderson and M.Bondart), Springer-Verlag, Berlin, 1981, Vol. 2, Chapter 5, pages 235 etseq., by n-butylamine titration against the Hammet indicator2-amino-5-azotoluene (pK_(a) =+2.0). The catalysts were dried beforehandat 200° C. and 0.01 mbar. The solvent used was benzene.

For the determination of its acidity, the parti-cular catalyst wassuspended in benzene and titrated with n-butylamine in the presence ofthe indicator. The indicator is yellow in its basic form and changes itscolor to red (acidic form) as soon as it is adsorbed onto the surface ofthe catalyst. The titer of n-butylamine which is required to restore theyellow color of the indicator is a measure of the concentration of theacid centers of acidity PK_(a) <+2 in the catalyst, expressed in mmol/gof catalyst or milliequivalent (mval)/g of catalyst, and hence of itsacidity.

Determination of the molecular weights

The average molecular weight (M_(n)) of the THF/butynediol copolymersand of the PTHF was determined by terminal group analysis by ¹ H-NMRspectroscopy. M_(n) is defined by the equation in which c_(i) is theconcentration of the individual polymer species in the polymer blendobtained and in which M_(i) is the molecular weight of the individualpolymer species.

    M.sub.n =Σc.sub.i /Σ(c.sub.i /M.sub.i)

The THF/butynediol copolymers obtained by polymerization of THF in thepresence of but-2-yne-1,4-diol show the following signals in the ¹ H-NMRspectrum (the chemical shift data relate to the signal maximum; solvent:CDCl₃): signal a: 4.3 ppm; b: 4.2 ppm; c: 3.6 ppm; d: 3.5 ppm, e: 3.4ppm; f: 1.6 ppm.

As shown in the formula 1, these signals can be assigned to the protonsindicated. The areas of the signals a, c and e were used for determiningthe molecular weight.

    HO-CH.sup.c.sub.2 --CH.sup.f.sub.2 --CH.sup.f.sub.2 --CH.sup.c.sub.2 --O--. . . --O--CH.sup.c.sub.2 --CH.sup.f.sub.2 --CH.sup.f.sub.2 --CH.sup.d.sub.2 --O--CH.sup.b.sub.2 --C═C--CH.sup.a.sub.2 --OH        (I)

EXAMPLES Batchwise THF polymerization in the presence ofbut-2yne-1,4-diol Example 1

Catalyst A which had an acidity (pK_(a) <+2) of 0.17 mmol of acidcenters/g of catalyst was used in this example.

10 g of catalyst A in powder form, which had been dried beforehand for20 hours at 180° C./0.3 mbar to remove adsorbed water, were added to 20g of peroxide-free THF which contained 1.6% by weight ofbut-2-yne-1,4-diol and 30 ppm by weight of water under an argon gasatmosphere in a 100 ml glass flask having a reflux condenser. Thesuspension was stirred for 20 hours at 50° C. After this time, thecooled reaction mixture was filtered and the catalyst powder was washedwith three times 20 g of THF. The filtrates were combined and wereevaporated down at 70° C./20 mbar in a rotary evaporator and thentreated for 1 hour in a bulb tube at 150° C./0.3 mbar. 3.8 g ofcolorless THF/butynediol copolymer were obtained as distillation residue(yield: 19%, based on THF used). The copolymer had an average molecularweight M_(n) of 1850.

Examples 2 to 6

Examples 2 to 6 were carried out as described in Example 1, the variouscatalysts B to F being used. The resulting average molecular weightsM_(n) of the THF/butynediol copolymers, the yields achieved and theacidities of the catalysts used, which were determined by Hammettitration, are listed in Table 1.

                  TABLE 1                                                         ______________________________________                                                                 Acidity (pK.sub.a  <                                                                   Copol-                                           +2) ymer                                                                   Exam- Cata-  [mmol/g of yield M.sub.n                                         ple lyst Catalyst type catalyst] [%] (.sup.1 H-NMR)                         ______________________________________                                        2     B      Bleaching   0.07     15.9  2500                                      earth                                                                       3 C MoO.sub.3 --ZrO.sub.2 -- 0.10 14.2  720                                     PO.sub.4                                                                    4 D WO.sub.3 --ZrO.sub.2 0.12 13.2 1700                                       5 E WO.sub.3 --ZrO.sub.2 -- 0.12 18.0 1200                                      SO.sub.4.sup.2-                                                             6 F ZrO.sub.2 --SO.sub.4.sup.2- 0.13 16.8  950                              ______________________________________                                    

Batchwise THF polymerization in the presence of butane-1,4-diolComparative Example 1 (comparison with Example 4)

As described in Example 1, 20 g of THF which contained 0.15% by weightof butane-1,4diol and 30 ppm of water were heated at 50° C. for 20 hourswith 10 g of catalyst D in the form of 3×3 mm pellets which had beendried beforehand for 20 hours at 180° C./0.3 mbar. After the catalysthad been removed and the filtrate evaporated down under reduced pressureas described in Example 1, a polymeric evaporation residue was obtainedin a yield of only 4.1%, based on THF used. The molecular weight of thePTHF was 1700.

Continuous THF polymerization in the presence of but-2-yne-1,4-diolExample 7

A 250 ml fixed-bed reactor was filled, under argon, with 352 g (250 ml)of the ZrO₂ /SO₄ catalyst F dried for 24 hours at 180° C./0.3 mbar. Thepolymerization apparatus was filled with but-2-yne-1,4-diol-containingTHF (1.5% by weight of but-2-yne-1,4-diol). This reaction mixture wasfirst pumped over the catalyst for 24 hours at a reactor temperature of50° C. Thereafter, further but-2-yne-1,4-diol-containing THF (1.5% byweight of but-2-yne-1,4-diol) was fed in continuously at a catalystspace velocity of 0.04 kg of THF per 1 of catalyst per h. Thecirculation/feed ratio was about 40 and the reactor temperature was 50°C. The discharged polymerization mixture (730 g) obtained during a runtime of 72 hours was worked up. After unconverted THF had been distilledoff and the residue obtained had then been subjected to moleculardistillation at 150° C./0.3 mbar, the resulting distillation residuecomprised 80 g of a THF/butynediol copolymer which, according to the ¹H-NMR spectrum, had an average molecular weight M_(n) of 970 Dalton. Theaverage yield over the reaction time of 72 hours was 11%. A space-timeyield of 4.4 g of THF/butynediol copolymer 970 per 1 of catalyst per hwas obtained.

Continuous THF polymerization in the presence of butane-1,4-diolComparative Example 2 (comparison with Example 7)

A 250 ml fixed-bed reactor was filled, under argon, with 372 g (220 ml)of the MoO₃ -ZrO₂ catalyst C dried for 24 hours at 180° C./0.3 mbar. Thepolymerization apparatus was filled with butane-1,4-diol-containing THF(0.4% by weight of butane-1,4-diol). This reaction mixture was firstpumped over the catalyst for 24 hours at a reactor temperature of 50° C.Thereafter, further butane-1,4-diol-containing THF (0.4% by weight ofbutane-1,4-diol) was fed in continuously at a catalyst space velocity of0.04 kg of THF per 1 of catalyst per h. The reacted polymerizationmixture (725 g) obtained during a run time of 72 hours was worked up asdescribed in Example 7, by distilling off the unconverted THF andcarrying out molecular distillation. 49 g of PTHF which, according to ¹H-NMR spectrum, had an average molecular weight M_(n) of 980 Dalton wereobtained. The yield was 6.8%. A space-time yield of only 2.5 g of PTHF980 per 1 of catalyst per h was obtained.

Continuous THF polymerization in the presence of but-2-yne-1,4-diolExample 8

A 250 ml fixed-bed reactor was filled, under argon, with 333 g (250 ml)of the WO₃ -Zro₂ catalyst D dried for 24 hours at 180° C./0.3 mbar. Thepolymerization apparatus was filled with but-2-yne-1,4-diol-containingTHF (0.9% by weight of but-2-yne-1,4-diol). This reaction mixture wasfirst pumped over the catalyst for 24 hours at a reactor temperature of50° C. Thereafter, further but-2-yne-1,4-diol-containing THF (0.9% byweight of but-2-yne-1,4-diol) was fed in continuously at a catalystspace velocity of 0.32 kg of THF per 1 of catalyst per h. Thecirculation/feed ratio was about 10 and the reactor temperature was 50°C. The discharged polymerization mixture (1.9 kg) obtained during a runtime of 24 hours was worked up as described in Example 7, by distillingoff the unconverted THF and carrying out molecular distillation. 185 gof a THF/butynediol copolymer which, according to ¹ H-NMR spectrum, hadan average molecular weight M_(n) of 2500 Dalton were obtained. Theyield was 10%. A space-time yield of 32 g of THF/butynediol copolymer2500 per 1 of catalyst per h was obtained.

Example 9

The continuous THF polymerization described in Example 8 and effectedover the catalyst D was continued under otherwise identical reactionconditions with a feed which contained 2.0% by weight ofbut-2-yne-1,4-diol in THF, at a catalyst space velocity of 0.16 kg ofTHF per 1 of catalyst per h. After the THF conversion had stabilized,the discharged reaction mixture (2.9 kg) obtained during a run time of72 hours was collected. After working up and molecular distillation asdescribed in Example 7, 210 g of THF/butynediol copolymer were isolated,said copolymer having an average molecular weight M_(n) of 1180according to the ¹ H-NMR spectrum. The yield was 7% based on THF used. Aspace-time yield of 11 g of THF/butynediol copolymer 1180 per 1 ofcatalyst per h was obtained.

Example 10

The continuous THF polymerization described in Example 9 and effectedover the catalyst D was continued under otherwise identical reactionconditions with a feed which contained 1.5% by weight ofbut-2-yne-1,4-diol in THF, at a catalyst space velocity of 0.16 kg ofTHF per 1 of catalyst per h. After the THF conversion had stabilized,the discharged reaction mixture (2.9 kg) obtained during a run time of72 hours was collected. After working up and molecular distillation asdescribed in Example 7, 280 g of THF/butynediol copolymer were isolated,said copolymer having an average molecular weight M_(n) of 1620according to the ¹ H-NMR spectrum. The yield was 10% based on THF used.A space-time yield of 16 g of THF/butynediol copolymer 1620 per 1 ofcatalyst per h was obtained.

As shown by the above examples, the novel process leads to asubstantially higher space-time yield, in conjunction with higher THFconversions, than a conventional process in which the telogen used isbutane-1,4diol instead of but-2-yne-1,4-diol.

HYDROGENATION EXAMPLES Batchwise hydrogenation of THF/butynediolcopolymers to PTHF Example 11

In a 50 ml metal autoclave, 5 g of a THF/butynediol copolymer preparedsimilarly to Example 1, in 10 g of tetrahydrofuran, were hydrogenatedwith hydrogen using 2 g of Raney nickel at 100° C. and 40 bar for 6hours. After the catalyst had been separated off and the solventdistilled off at reduced pressure, 4.8 g of residue were obtained. Thisresidue was furthermore subjected to distillation in a bulb tube at 150°C./0.3 mbar. The distillation residue obtained was a colorlesspolytetrahydrofuran which, according to the ¹ H-NMR spectrum, containedno C--C triple bonds. The PTHF thus obtained had an average molecularweight M_(n) of 1900.

Example 12

10 g of a THF/butynediol copolymer prepared similarly to Example 6 anddissolved in 10 g of tetrahydrofuran were hydrogenated with hydrogenusing 4 g of a nickel- and copper-containing supported catalyst(prepared according to U.S. Pat. No. 5 037 793; nickel content 50%,calculated as NiO; copper content 17%, calculated as CuO; molybdenumcontent 2%, calculated as MoO₃ ; carrier: ZrO₂ 31% by weight; catalystform: 6×3 mm pellets) at 120° C. and 40 bar for 6 hours. The catalysthad been activated beforehand in a stream of hydrogen at 200° C. for 2hours. Working up and molecular distillation of the dischargedhydrogenation mixture were carried out as described in Example 11. 9.2 gof colorless polytetrahydrofuran were obtained, which, according to the¹ H-NMR spectrum, contained no C--C triple bonds and whose residualdouble bond content was <0.5%. The PTHF thus obtained had an averagemolecular weight M_(n) of 1020.

Example 13

As described in Example 11, 10 g of a THF/butynediol copolymer preparedsimilarly to Example 2 and dissolved in 20 g of tetrahydrofuran werehydrogenated with hydrogen over 4 g of a calcium-containing palladium onalumina supported catalyst (prepared by impregnating an Al₂ O₃ /CaOcarrier, obtained by kneading moist Al₂ O₃ and CaO, drying at 120° C.and calcining at 550° C., with an aqueous palladium nitrate solution;palladium content 0.6% by weight, calculated as Pd; calcium content 20%by weight, calculated as CaO; 79.4% by weight of Al₂ O₃) in the form of4 mm extrudates at 120° C. and 40 bar for 8 hours. Working up anddistillation were carried out as described in Example 11. 9.1 g ofcolorless PTHF which had an average molecular weight M_(n) of 2600 wereobtained. According to the ¹ H-NMR spectrum, the product contained noC--C triple bonds, and the residual content of C--C double bonds was<3%.

Example 14

As described in Example 11, 5 g of a THF/butynediol copolymer preparedsimilarly to Example 4, in 10 g of tetrahydrofuran, were hydrogenatedwith hydrogen using 2 g of a palladium on alumina catalyst (prepared byimpregnating Al₂ O₃ extrudates with an aqueous palladium nitratesolution, drying at 120° C. and calcining at 440° C.; palladium content0.5% by weight, calculated as Pd; 99.5% by weight of Al₂ O₃) in the formof 4 mm extrudates at 140° C. and 40 bar for 6 hours. The catalyst hadbeen activated beforehand in a stream of hydrogen for 2 hours at 150° C.Working up and bulb-tube distillation of the discharged hydrogenationmixture were carried out as described in Example 11. 4.5 g of colorlessPTHF were obtained, which, according to the ¹ H-NMR spectrum, containedno C--C triple bonds and had a residual double bond content of less than2%. The molecular weight M_(n) was 1750.

We claim:
 1. A process for the preparation of copolymers oftetrahydrofuran and but-2-yne-1,4-diol by catalytic polymerization oftetrahydrofuran, which comprises carrying out the polymerization over aheterogeneous acidic polymerization catalyst which has acid centers ofacidity pK_(a) <+2 in a concentration of at least 0.005 mmol/g ofcatalyst, in the presence of but-2-yne-1,4-diol, wherein thepolymerization catalyst used is a member selected from the groupconsisting of:a) a supported catalyst which contains a catalyticallyactive amount of an oxygen-containing tungsten or molybdenum compound ora mixture of these compounds on an oxide carrier, b) a sulfate-dopedzirconium dioxide, c) a bleaching earth, and d) a perfluorinated polymercontaining α-fluorosulfonic acid groups.
 2. A process as claimed inclaim 1, wherein, in the case of the catalysts (a), calcination has beeneffected at from 500 to 1000° C. after application of the precursorcompounds of the oxygen-containing molybdenum or tungsten compounds tothe carrier precursor.
 3. A process as claimed in claim 1, wherein theoxide carrier used is zirconium dioxide, titanium dioxide, hafniumoxide, yttrium oxide, iron oxide, alumina, tin oxide, silica, zinc oxideor a mixture of these oxides.
 4. A process as claimed in claim 1,wherein the supported catalyst contains from 0.1 to 50% by weight,calculated as molybdenum trioxide or tungsten trioxide and based on thetotal weight of the catalyst, of molybdenum or tungsten.
 5. A process asclaimed in claim 1, wherein a catalyst which is additionally doped withoxygen-containing sulfur or phosphorus compounds is used.
 6. A processas claimed in claim 1, wherein zirconium dioxide or titanium dioxide isused as the carrier.
 7. A process as claimed in claim 1, wherein thebut-2-yne-1,4-diol is used in an amount of from 0.04 to 17 mol%, basedon tetrahydrofuran.
 8. A process as claimed in claim 1, wherein thepolymerization is carried out at from 0 to 100° C.
 9. A process for thepreparation of polyoxytetramethylene glycol, which comprises reacting acopolymer prepared by a process as claimed in claim 1 and comprisingtetrahydrofuran and but-2-yne-1,4-diol, in the presence of hydrogen atfrom 20 to 300° C. and from 1 to 300 bar over a hydrogenation catalyst.10. A process as claimed in claim 9, wherein a hydrogenation catalystwhich contains at least one element from group Ib, VIIb or VIIIb of thePeriodic Table of Elements is used.
 11. A process as claimed in claim 9,wherein a hydrogenation catalyst which contains at least one of theelements nickel, copper and palladium is used.
 12. A process as claimedin claim 9, wherein a heterogeneous hydrogenation catalyst is used. 13.A process for the preparation of copolymers of tetrahydrofuran andbut-2-yne-1,4-diol, which copolymers contain double bonds, whichcomprises subjecting the copolymer prepared by a process as claimed inclaim 1 and comprising tetrahydrofuran and but-2-yne-1,4-diol to partialhydrogenation over a hydrogenation catalyst.